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Backdropped by Popocatepetl Volcano, Mexico's second highest peak just 55 km southeast of Mexico City, a farner plows the land in San Nicolas de los Ranchos, in the state of Puebla, on May 14, 2013. The National Disaster Prevention Centre (CENAPRED) raised the alert level on Sunday to "yellow phase three" as the Popocatepetl continues to spew ash and smoke. Ronaldo Schemidt/AFP/Getty Images

General view of two ambulances at the San Nicolas de los Ranchos community near Popocatepetl volcano, in Puebla, Mexico, on May 12, 2013. According to a report by the National Center of Prevention of Disasters (CENAPRED) the yellow alert phase three is still in force. Jose Castañares/AFP/Getty Images

Clouds of ash and smoke are spewed from the Popocatepetl Volcano as seen from Santiago Xalitxintla, in Puebla, Mexico, on May 13, 2013. According to a report by the National Center of Prevention of Disasters (CENAPRED) the yellow alert phase three is still in force. Ronaldo Schemidt/AFP/Getty Images

View of Santiago Xalitxintla community with the Popocatepetl Volcano on the background, in Puebla, Mexico, on May 13, 2013. According to a report by the National Center of Prevention of Disasters (CENAPRED) the yellow alert phase three is still in force. Ronaldo Schemidt/AFP/Getty Images

A family walks in Santiago Xalitzintla community near Popocatepetl volcano, in Puebla, Mexico, on May 13, 2013. According to a report by the National Center of Prevention of Disasters (CENAPRED) the yellow alert phase three is still in force. Ronaldo Schemidt/AFP/Getty Images

The Popocatepetl Volcano, Mexico's second highest peak just 55 km southeast of Mexico City, is seen from Santiago Xalitxintla, in Puebla, on May 14, 2013 spewing a cloud of ash and smoke. The National Disaster Prevention Centre (CENAPRED) raised the alert level on Sunday to "yellow phase three". Ronaldo Schemidt/AFP/Getty Images

The Popocatepetl volcano spews ash and steam as seen from Santiago Xalitzintla, Mexico, Sunday evening, May 12, 2013. Seismic activity has increased at the Popocatepetl volcano near Mexico City, leading authorities to alert towns in two central states and the capital. (AP Photo/Marco Ugarte)

The Popocatepetl Volcano, Mexico's second highest peak just 55 km southeast of Mexico City, is seen from Santiago Xalitxintla, in Puebla, on May 14, 2013 spewing a cloud of ash and smoke. The National Disaster Prevention Centre (CENAPRED) raised the alert level on Sunday to "yellow phase three". Ronaldo Schemidt/AFP/Getty Images

Two women walk in San Nicolas de los Ranchos community near Popocatepetl volcano, in Puebla, Mexico, on May 12, 2013. According to a report by the National Center of Prevention of Disasters (CENAPRED) the yellow alert phase three is still in force. Jose Castañares/AFP/Getty Images

Two ambulances remain parked at the entrance to San Nicolas de los Ranchos community near Popocatepetl volcano, in Puebla, Mexico, on May 12, 2013. According to a report by the National Center of Prevention of Disasters (CENAPRED) the yellow alert phase three is still in force. Jose Castañares/AFP/Getty Images

Backdropped by Popocatepetl Volcano, Mexico's second highest peak just 55 km southeast of Mexico City, a man rides his bicycle in San Nicolas de los Ranchos, in the state of Puebla, on May 14, 2013. The National Disaster Prevention Centre (CENAPRED) raised the alert level on Sunday to "yellow phase three" as the Popocatepetl continues to spew ash and smoke. Ronaldo Schemidt/AFP/Getty Images

Photos: Smoke billows from Mexico’s Popocatepetl Volcano

Mexico's Popocatepetl Volcano continues to spew ash and smoke in the state of Puebla, just 55 km southeast of Mexico City, May 14, 2013. The National Disaster Prevention Centre (CENAPRED) raised the alert level on Sunday to "yellow phase three."